Qilianshanite

Formula: NaHCO3.H3BO3.2H2O

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: Biaxial

Optical sign: -

Refractive indices: α = 1.351, β = 1.459, γ = 1.486

Bireflectance/Birefringence δ: 0.135

2V angle: 48° (calculated), 50° (measured)

Dispersion: Medium, r < v

Optical orientation: α = b, β Ù a = 1° , z Ù c = 9°

Optical axial plane:

 

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